In a submarine warfare training applications it is known to deploy a device in the water to simulate a submarine periscope mast extended above the water in order to train radar operators to find small radar targets. A submarine mast simulator is shown by Horton in U.S. Pat. No. 6,845,728, entitled TOWABLE SUBMARINE MAST SIMULATOR. Horton describes a tow body formed by a hydrodynamically shaped hollow shell formed with a nose, a tail and a plurality of stabilizer fins extending radially from the tail. The shell shape and stabilizer fins are configured to minimize drag and to stabilize the orientation of the tow body as it is towed by an unmanned underwater vehicle (UUV). The shell attaches to the UUV underwater vehicle by a tow line or cable to tow the shell at a desired speed, along the water surface, or submerged at a desired depth below the water surface.
Horton's tow body is equipped with a variety of submarine simulating features including a simulated submarine mast that generates a wake in the water and provides a visual and radar profile similar to that of a submarine mast extended above the water. The tow body also includes a combustion chamber that generates simulated infrared and chemical vapor emissions of a submarine. The simulated submarine mast includes a rigid but hollow cylindrical lower portion pivotally attached to the shell. The mast upper portion comprises an inflatable elastomeric tube that is filled by air to deploy the mast visual and radar simulator element vertically extended above the water surface. In a non-operating position the mast upper portion is deflated and coiled and the mast lower portion pivoted to a horizontal orientation for storage inside the shell. However, the submarine mast simulator described by Horton is complex and costly. It includes a mast pivoting motor and gears, an air pump to inflate the elastomeric tube and numerous automated electrical and mechanical control elements to raise and lower the mast as required. Much of the complexity of the Horton device relates to vertically extending the radar target above the water. Meanwhile, there is a need for a simpler lower cost device.
In another example, a target training device is shown by Yoshikawa et al. in U.S. Pat. No. 4,215,862, entitled WATER SURFACE TOWED TARGET. Yoshikawa et al. describe a towed target formed by a torpedo shaped underwater towed member supporting a target pole or mast extending above the water surface. The towed member is towed by a ship and the target pole includes a spherical radar reflector (Lunenburg lens) supported at its top end. In order to stabilize the towing characteristics of the Yoshikawa et al. device and particularly to keep the mast vertically oriented, the towed member is configured with a submerged ballast weight, a plurality of target support and stabilizing members. Again, much of the complexity of the Yoshikawa et al. device relates to vertically extending the radar target above the water.
Applicants have recognized that a radar target disposed substantially horizontally along the water surface can be detected by an airborne radar system and may be used to train airborne radar operators in submarine warfare. This realization allows the use of a simplified and less costly radar target to simulate the radar cross-section of a submarine mast but without the need to support the target vertically extended above the water surface. In addition, there is a need in the art of submarine warfare training to provide a submerged radar target, e.g. being towed at a submerged depth of 100 feet below the water surface and this need is not addressed by in the prior art.
A horizontally disposed radar target is disclosed by Yonover in U.S. Pat. No. 5,421,287 entitled VISUAL LOCATING DEVICE FOR PERSONS LOST AT SEA OR THE LIKE. Yonover discloses a streamer rolled up for storage and attached to a flotation device such as might be worn by a distressed person in water. The streamer is formed of a thin polyethylene material outstretched flat on the water surface. The streamer is coated with one or more materials selected to make the streamer visible from an aircraft. However, even if the streamer of Yonover had radar reflective material, it would not be effective for detection by radar in an airplane because the streamer is essentially flat resting on the water surface with water flowing over it.